Q.Explain extraction of copper from copper pyrite.

Blister copper is impure (~98%) copper from the converter stage that gets a blistered surface as dissolved SO2 escapes on solidifying.

In the extraction of copper from copper pyrites, after roasting, the matte (containing Cu2S and FeS) is charged into a silica-lined converter along with silica and a blast of air. In this converter:

• FeS is oxidised and removed as FeSiO3 (slag).
• The remaining Cu2S undergoes oxidation to give copper metal, releasing SO2 gas: 2Cu2S + 3O2 -> 2Cu2O + 2SO2 2Cu2O + Cu2S -> 6Cu + SO2

The copper obtained at this stage is about 98% pure and still contains dissolved SO2 gas along with small amounts of impurities. When this molten copper is allowed to cool and solidify, the dissolved SO2 gas escapes from within the solidifying metal, causing the surface to develop blister-like swellings/bumps.

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Silica acts as an acidic flux in copper extraction, converting the FeO impurity into a molten slag that floats off.

In the extraction of copper from copper pyrites (CuFeS2), after roasting, the ore is converted into a mixture of Cu2S and FeO along with unreacted sulphides. This roasted product is then mixed with silica (SiO2) and heated in a reverberatory furnace (smelting).

Silica is an acidic flux. It reacts with the basic iron oxide (FeO) impurity present in the roasted ore to form a low-melting, fusible slag of iron silicate:

FeO + SiO2 → FeSiO3 (iron silicate slag)

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Blister copper is the crude ~98% pure copper formed after the Bessemer-converter self-reduction step, named for the blister-like surface left by escaping SO2 gas.

Formation: In the extraction of copper from copper pyrites (CuFeS2), after roasting and smelting, a matte containing Cu2S and FeS is obtained. This is charged into a Bessemer converter with silica lining. Air is blown through the molten matte: FeS is oxidised and removed as FeSiO3 slag, and Cu2S is partly oxidised to Cu2O. The Cu2O and remaining Cu2S then undergo self-reduction (auto-reduction):

$2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2\uparrow$

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